The invention relates to motor vehicles in general, and more particularly to improvements in methods of and in means for controlling the speed of a motor vehicle during coasting. Still more particularly, the invention relates to improvements in methods of and in means for controlling the coasting speed of a motor vehicle wherein the power train employs a prime mover (such as an internal combustion engine) and an infinitely variable ratio transmission which serves to transmit torque (a) from the prime mover to the wheels when the vehicle is driven by the prime mover and (b) from the wheels to the prime mover while the vehicle is coasting.
Motor vehicles employing power trains of the above outlined character are disclosed, for example, in German patent No. 195 46 294. The automatic infinitely variable ratio transmission in the power train of the patented motor vehicle is a so-called CVT employing two adjustable pulleys or sheaves and an endless flexible torque transmitting element which is trained over the pulleys. An advantage of such transmissions (in comparison with transmissions having limited numbers of gear ratios) is that automatic adjustments of the transmission ratio render it possible to achieve substantial savings in fuel.
A drawback of numerous power trains in presently known motor vehicles is that, during coasting (i.e., when the vehicle is in motion while the wheels roll along a downwardly sloping surface and while the operator keeps her or his foot off the gas pedal), the vehicle is or is likely to be accelerated to a speed which often exceeds a maximum permissible value.
An object of the present invention is to provide a motor vehicle with a power train which employs an infinitely variable ratio transmission and the speed of which during coasting is regulated in a novel and improved way.
Another object of the invention is to provide novel and improved controls which automatically influence the operation of the power train when the motor vehicle is coasting.
A further object of the invention is to provide the power train of a motor vehicle with automatic controls for the speed of the motor vehicle during coasting.
An additional object of the invention is to reduce the likelihood of accidents and/or damage to motor vehicles during coasting.
Still another object of the invention is to provide a power train which renders it possible to regulate the vehicle speed during coasting and which can be installed in existing motor vehicles.
A further object of the instant invention is to provide a novel and improved method of automating the operation of the power train in a motor vehicle while the vehicle is coasting.
Another object of the invention is to provide a novel and improved method of preventing excessive acceleration of a motor vehicle during travel along a downwardly sloping road surface and while the operator of the motor vehicle abstains from influencing the speed of the vehicle such as by permitting operation of the prime mover at idling speed.
One feature of the present invention resides in the provision of a motor vehicle which comprises an infinitely variable ratio transmission including a rotary input member and a rotary output member (at least one of these members can constitute a shaft), at least one wheel arranged to receive torque from the output member when the prime mover drives the input member of the transmission and to transmit torque to the prime mover by way of the input and output members when the motor vehicle is coasting, and operator-manipulatable actuating means for influencing the prime mover. Such actuating means includes monitoring means arranged to ascertain at least one variable parameter of the motor vehicle, and the vehicle further comprises means is for infinitely varying the ratio of the transmission; such infinitely varying means includes means for at least temporarily regulating the transmission ratio to prevent an increase (or an excessive increase) of vehicle speed when the motor vehicle is coasting.
The monitoring means can include a sensor (e.g., a suitable tachometer generator) which is arranged to ascertain the speed of the motor vehicle and to influence the aforementioned means for infinitely varying the ratio of the transmission so as to change the transmission ratio in a sense (i.e., in a direction) to reduce the speed of the motor vehicle while the vehicle is coasting and its speed tends to increase so that, as a result of the change of transmission ratio, the speed of the motor vehicle remains at least substantially constant. The monitoring means of such power train can further include means for detecting absence of manipulation of the actuating means by the operator of the motor vehicle; such absence of manipulation detecting means can include a switch or another suitable sensor which monitors the position of the gas pedal and transmits a signal at least when the gas pedal is not depressed.
In accordance with a modification, the monitoring means can include a sensor which is arranged to ascertain the speed of the motor vehicle and to influence the means for infinitely varying the ratio of the transmission in order to change the ratio of the transmission while the motor vehicle is coasting so that the speed of the motor vehicle is reduced at least until the transmission ratio reaches a preselected value. Such monitoring means can further include the aforementioned means for detecting absence of manipulation of the actuating means by the operator of the motor vehicle.
In accordance with another modification which can be put to use when the prime mover is a variable-RPM prime mover (such as a combustion engine), the monitoring means includes a sensor which is arranged to ascertain the speed of the motor vehicle and to influence the means for infinitely varying the ratio of the transmission in order to change the transmission ratio when the motor vehicle is coasting in such a way that the speed of the motor vehicle remains at least substantially constant until the RPM of the prime mover reaches a predetermined threshold value. The monitoring means can further include means for detecting absence of manipulation of the actuating means by the operator of the motor vehicle.
Another feature of the instant invention resides in the provision of a method of operating a variable-speed motor vehicle wherein a prime mover (such as an internal combustion engine) drives an infinitely variable ratio transmission when the motor vehicle is not coasting, wherein the infinitely variable ratio transmission drives the prime mover when the vehicle is coasting, and wherein an operator-manipulated actuating means is arranged to influence the prime mover and embodies means for monitoring at least one variable parameter of the motor vehicle. The method comprises at least one step, namely the step of infinitely varying the ratio of the transmission to at least temporarily regulate the transmission ratio in a sense to prevent an increase of the speed of the motor vehicle when the vehicle is coasting.
The method can further comprise the steps of monitoring the speed of the motor vehicle and altering the ratio of the transmission in a sense to reduce the speed of the motor vehicle when the motor vehicle is coasting and its speed tends to increase so that the speed of the motor vehicle during coasting remains at least substantially constant.
Alternatively, the improved method can comprise the additional steps of monitoring the speed of the motor vehicle and of influencing the step of varying the ratio of the transmission to thus change the ratio of the transmission when the motor vehicle is coasting with the result that the speed of the motor vehicle is reduced at least until the transmission ratio is changed to a predetermined value.
Still further, the improved method can comprise the additional steps of monitoring the speed of the motor vehicle and of influencing the step of varying the transmission ratio to thus change the transmission ratio when the motor vehicle is coasting with the result that the speed of the motor vehicle remains at least substantially constant until the RPM of the prime mover reaches a predetermined threshold value.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved motor vehicle itself, both as to its construction and the mode of operation of its power train, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.